ATtiny85 high-voltage progamming

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Does anybody know exactly what the 12v does during high-voltage programming the ATtiny85

The data sheets states...

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1. Set Prog_enable pins listed in Table 20-14 to "000", RESET pin and VCC to 0V.
2. Apply 4.5 - 5.5V between VCC and GND. Ensure that VCC reaches at least 1.8V within the next 20 μs.
3. Wait 20 - 60 μs, and apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10 μs after the High-voltage has been applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable[2] pin to avoid drive contention on the Prog_enable[2]/SDO pin.
6. Wait at least 300 μs before giving any serial instructions on SDI/SII.
7. Exit Programming mode by power the device down or by bringing RESET pin to 0V.

Step 3 applies 12v and the way I read it the HV stays there until step 7 when programming is done, but this isn't actually stated (although of course if you power the chip down presumably the 12v goes as well).

It's just as possible that the 12v is no longer required after entering program mode and it is removed.

So to put my question another way, does anyone know if the presence of 12v can be used to detect that the chip is being programmed?

Rob

Scattered showers my arse -- Noah, 2348BC.
Rob Gray, old fart, nature photographer, embedded hardware/software designer, and serial motorhome builder, www.robgray.com

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Well you could obviously use your meter or scope to see what the STK500/STK600/Dragon do when they are doing HV programming but you'll find that the +12V remains applied during the entire session I believe.

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Thanks, I don't have access to my test gear at present but I know that for example when ISP programming the STK500 has a short glitch on RST at the start, if you were detecting this with clocked logic there could be a problem. For the moment I'll continue designing on the assumption that the signal is clean but cover my arse in case it's not.

Scattered showers my arse -- Noah, 2348BC.
Rob Gray, old fart, nature photographer, embedded hardware/software designer, and serial motorhome builder, www.robgray.com

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Why do you want HVSP ?

The Tiny85 works fine with regular ISP.

If you choose to blow the RSTDSBL fuse, you will need to recover the chip.
But most Tiny's with RSTDSBL run fairly simple programs. You write it once and forget about ever re-programming. Chuck it away and start again.

Of course, if you do not blow RSTDSBL you can re-program it as much as you like.

David.

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Quote:
Why do you want HVSP ?
The Tiny85 works fine with regular ISP.

True and that's how I currently use them, but I've got a few things in mind that will need all 6 IO pins, simple programs but still needs all possible IO.

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You write it once and forget about ever re-programming. Chuck it away and start again.

Even simple programs can have 50 interations (well mine do anyway :)), I can't afford to bin that many chips and even if I could it can take me weeks to get replacements.

Rob

Scattered showers my arse -- Noah, 2348BC.
Rob Gray, old fart, nature photographer, embedded hardware/software designer, and serial motorhome builder, www.robgray.com

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I would normally develop and test the code on a chip with more i/o. Then port to the Tiny85.

Since you have a STK500, you can watch exactly what happens with HVSP. Or if the worst comes to the worst, read the data sheet.

I would guess that the /RESET pin is the only one that sees 12V. i.e. the other pins only see 5V.

But it is your chip, you can do the reading.

David.

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I would normally develop and test the code on a chip with more i/o. Then port to the Tiny85.

But what if you need to develop with the chip in-circuit and in an environment too complex to reproduce on a breadboard?

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Since you have a STK500, you can watch exactly what happens with HVSP.

I will, but I don't have access to it at present and thought somebody may know for sure from previous experience.

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Or if the worst comes to the worst, read the data sheet.

Excerpt in the OP, but it is ambiguous to my mind.

Quote:
I would guess that the /RESET pin is the only one that sees 12V. i.e. the other pins only see 5V.

That's correct.

Rob

Scattered showers my arse -- Noah, 2348BC.
Rob Gray, old fart, nature photographer, embedded hardware/software designer, and serial motorhome builder, www.robgray.com